Circuit protector



Sept. 14, 1948. H. LAMONT CIRCUIT PROTECTOR Filed July 17. 1946 l ul INVEN TOR.

Patented Sept. 14, 1948 UNITED STATES PATENT OFFICE 2,448,238 cmcurrrao'rac'roa Lewis B. Lamont, Chicago, Ill. Application July 17, 1946,Serial No. 684,210

' c; Claims. (01. 200-88) The present invention relates to a protectivedevice for preventing open circuit conditions to remain when there is abreak or overload in a high tension circuit-also preventing hazardousarcing to ground caused by water, snow or any foreign matter. The deviceis particularly applicable as' a safety device for protectingtransformers of the current limiting type from the danger of havingtheir secondary open circuited and kept in this position. Transformersof the type herein referred to have the characteristic of building upthe secondary voltage as theresistance across the secondary increases.

The present invention contemplates a device of this character wherein asudden increase in voltage across the high tension terminals will resultin establishing an arc or spark discharge or short circuit which ismaintained so long as the high tension terminals remain energized. Thedevice is so arranged that if the current supply is cut off and thetrouble remedied, the device automatically resets itself so as to beready in the event of a further open circuit, overload or groundcondition, to again act to protect against excessive high voltages.

Specifically, the present device is of particular advantage withtransformers of the type herein above referred to. It will be readilyapparent, however, that it is not so limited, and may be used whereverit is desirable to protect against excessive rises in voltage betweentwo terminals by establishing a low resistance path or substantial shortcircuit across the terminals and releasing the short circuit path whenthe current is shut off.

The features and advantages of the present invention will appear morefully as the description proceeds, reference being had to theaccompanying drawings wherein a preferred form of the invention isshown. It is to be understood, however, that the drawings anddescription are illustrative only, and are not to be taken as limitingthe invention except insofar as it is limited by the claims.

In the drawings:

Figure 1 is a cross sectional view through a device embodying thepresent invention Figure 2 is a top plan view of the device;

Figure 3 is an end view of the device; and

Figure 4 is a sectional view on the line 4-4 of Figure 1.

Referring now to the drawings, in this device 'two terminals 8- 8 areadapted to be connected to the secondary of a transformer I such as thecurrent limiting high tension transformers customarily used for thepurpose of stepping up the voltage from its normal commercial value tothe necessary high voltage for energizing gaseous conduction signsandcold cathode lighting tubes and terminal 1 is connected to groundthrough a ground post when transformers are mid point grounded. Theterminals lead through a porcelain housing 8 for the safety device whichis the subject matter of the present invention.

The present invention concerns itself with a mechanism by which the hightension terminals 8-8 and 1 will be connected by a low resistance path,if at any time excessive voltage is built up between them. The studposts [0 carry conducting plates II which are held in place by nuts i2.The terminals 8 are connected to the stud posts I8 by flexible wires.The plates ll constitute terminal members for'the purpose ofestablishing the low resistance path between the terminal stud posts 10.Each plate has a portion l3 which forms part of the initial shortcircuiting mechanism. Since this mechanism is a duplicate for each ofthe plates i I, it is believed to be sufficient to describe one of themechanisms in detail. The short circuiting mechanisms !4 and I5 aremounted on a support i8 which is connected to ground terminal I. Themechanisms comprise two coiled bimetallic strips which are suitablyfastened to the grounded support IS. The bimetal strips l4 and i5 are soarranged that they are directly connected to the support l8 and arecoiled at their upper ends and joined at the center of the coil whichspirals outwardly and downwardly to provide contact arms I! and I8. Thearms I! and 18 have contacting electrodes l8 and 20 on their free ends.The arrangement of each bimetal strip is such that if it is heated. thefree end is caused to swing out from the vertical position, as shown bydotted line in Figure 1, thus bringing the contact elements I! and 28 incontact with plates II. In the normal operation there is of course nocurrent flowing to the bimetallic strips I4 and I5, and therefore thereis no heat condition that would cause them to swing the contacts l9 and20 into an engagement with plates ll. Normal rise or fall of temperatureto which the device is subjected would not cause any such action. Meansare provided whereby an excessive rise in voltage between the terminals8-8 or 8 and I will establish a conducting path for current to flow andheat up the bimetallic strips. Each plate ii, near its upper end,carries an electrostatically responsive leaf 2|. The leaf 2| as shown,is hinged to the upper portion of the plate i i, so that they can swingout toward each other and the support I8. For practical purposes, I havefound a light metal strip, such as a thin aluminum strip, is entirelysatisfactory for the leaf 2 I.

In the normal operation of the device there is a direct conduction pathestablished between the terminals 88 through the gaseous discharge tube4 which is being energized from the transformer 5. If this conductingpath is broken or disturbed, a charge builds up on each terminal, whichcharge increases as the voltage rises. Since the charge on the studposts I is opposite in polarity, the leaves II are attracted to eachother and swing outwardly to the position shown by the dotted line,until they come so close to the support l6 as to cause a spark dischargeto start between their tips and the support. This discharge, once it isstarted, quickly causes an are between the supporting plate Ii and thesupport i6, resulting in generation of a substantial amount of heatwithin the housing, and particularly adjacent to the bimetallic stripsI4 and ii.

The heat generated from the are which was lust described causes thecontacts is and to move toward the leaves 2i and plates II, and close acircuit between plates H and the support i8. 2

01' course when the contact elements engage,

moment the contacts I! and 20 separate fromthe plates I I, the voltagebuilds up in the secondary of the transformer 5 to start the are betweenthe contacts. The heat generated due to current flowing across this arcwill overcome the separation of the contacts by heating the strips ll.and i5. Thus the strips I4 and i5 continue to move toward and away fromthe closed circuit position, and maintain a protecting circuit ofcomparatively low resistance between the terminals 8-8 and 1, until suchtime as the current supplied to them is cut oil. When this happens, thestrips H and [5 are returned to the normal position. The leaves 2| ofcourse return to their normal resting position as soon as the arc isestablished and the electrostatic difference becomes too small to holdthem in position.

The space in between plates ii and the support I6 is varied dependingupon the necessary voltage at which'the transformer operates. with ahigh secondary voltage necessary for operation, the plates ii andsupport l6 are spaced further apart than with a lower voltage. In allevents, the spacing between the plates ii and support i6 is much greaterthan is necessary to prevent the spark discharge starting between theleaves 2| and the ground support It, in preference to current flowingthrough the gaseous discharge tube that is being energized.

When the transformer is first energized to start the tube in operation,the leaves 2| will flutter slightly because of the electrostaticdifference between them, but will not come close enough to each other orthe support I! to establish an arc discharge. Once current is flowing inthe gaseous discharge tube. there is no tendency for the leaves to swingtoward each other unless an open circuit or circuit to ground raises thevoltage between plates H or between either plate and the support l6. Itis characteristic of these transformers, when a ground occurs on eitherside of the mid-point, that the opposite side will become overloaded,causing the voltage to rise. This in turn causes an electrostaticdiflerence between the plate H and support II, which in turn causes oneleaf 2! to swing toward the support is establishing an arc as heretoforedescribed. The are sets up heat so as to move the adjacent bimetalstrip. The bimetai strips are offset so that the section grounded (whichhas no arc) closes first, then the other section closes and theoperation is as heretofore described. If the transformer is notmid-point grounded then both leaves 2| will swing toward the support ii,but only on open circuit or overload.

All parts of this protective device are so constructed as to resist thecorrosive effects which result from the acid formed by an arc dischargethrough the air. The housing is of porcelain, the elements used for theseveral parts of the safety device are stainless steel for the plates IIand parts l0 and i6, aluminum is used for the leaves I! and cadmiumplating is used upon the bi-metallic elements I and ii. In addition, theterminal posts H and 1 are made of stainless steel or other suitablemetal that resists acid corrosion. .The present invention has been foundto be quite sensitive to voltage changes without a correspondingsensitivity to barometric conditions. Heretofore, safety devicesconsisting of two spaced stationary ball electrodes have been used toprovide an arc discharge path parallel to the tubing across thetransformer secondary. Such a. device, however, is quite responsive tobarometric conditions surrounding the device. Dry air increases and wetair decreases the breakdown resistance of the discharge path.

With the present safety device it is possible to have a very narrowrange between operating voltage and the voltage at which the safetydevice will act. For example, most gaseous tube transformers arerequired by the Underwriters Laboratories to be limited to 15,000 voltson open circuit. Many operators have sumcient tubing to require 12,000to 13,000 volts starting voltage. The safety device has to operate upona voltage rise of less than 2,000 volts and yet be reliable in all kindsof weather.

The electrostatic principle employed here makes it possible to operatewithin a small volt age range. It is well known that the attractionbetween two electrified bodies are in the inverse radio of the square oftheir distance apart. In our device as the leaves swing toward thegrounded support and each other a greater amount of force is required toovercome the 7 weight of the leaves.

The repulsion of the leaf by its mounting decreases, but the attractionby the opposite leaf or support I in increased. 1 utilize these factorsin obtaining a sturdy. reliable safety device which will act to protecthigh tension lines against excessive rises in voltage.

Figure 1 shows notches 22 and slots 23 in the porcelain, whereby onestud post i0 and its mechanism can be moved so as to operate ondifferent transformer voltages, the support I. must also be moved tocorresponding slots 24 in the base of the housing.

From the foregoing description it is believed that the construction andoperation of my invention will be readily apparent to those skilled inthis art. Having thus described my invention, what I claim as new anddesire to secure by Letters Patent is:

1. A safety device for protecting a current source against open circuitground or overload, said device comprising, in combination, spacedconducting members adapted to be connected to the opposite terminals ofthe current source, a grounded conducting member between the first namedmembers, an electrostatic charge responsive leaf connected with at leastone member and being free to move in response to the attraction ofopposite electrostatic charges on said members and shorten the gapbetween them to the point where spark discharge occurs across the gapbetween a pair of said members, a retractile gap bridging elementconnected to at least one of said members and operable in response tothe resulting current flow from the discharge between the members toestablish and maintain a low resistance path between said members solong asthe current flow continues.

2. A safety device for protecting a current source against open circuitground'or overload, said device comprising, in combination, spacedconducting members adapted to be connected to the opposite terminals ofthe current source, a grounded conducting member between the firstname'd members. an electrostatic charge responsive leaf suspended fromeach of the first named members and being free to move in response tothe attraction of opposite electrostatic charges on said first namedmembers and shorten the gap between them and the grounded member to thepoint where spark discharge occurs across the gap, retractile gapbridging elements connected to said grounded member and operable inresponse to the current flow from the discharge between the members toestablish and maintain a low resistance path between said groundedmember and said first named members so long as the current flowcontinues.

3. A safety device for protecting a current source against open circuitground or overload, said device comprising, in combination, spacedconducting members adapted to be connected to the opposite terminals ofthe current source, a third grounded member between said first namedmembers, an electrostatic charge responsive leaf connected with at leastone member and being free to move in response to the attraction ofopposite electrostatic charges on said first named members and shortenthe gap between it and the grounded member to the point where sparkdischarge occurs across the gap, retractile bi-metallic discharge heatedthermostatic strips connected to said grounded member and operable inresponse to the resulting heat from the arc discharge to establish andmaintain a low resistance path between said first named members and thegrounded member.

4. A safety device of the character described comprising a housing,spaced conducting members therein adapted to be connected to oppositesides of a high voltage source, an intermediate grounded conductingmember, an electrostatic charge responsive leaf suspended from each ofthe first named members to swing toward the grounded member to establishan arc discharge between said members in said housing, and heatresponsive elements on said grounded member movable toward the othermembers in response to the heat from said are discharge to establish alow resistance path between the grounded member and said first namedmembers.

5. A safety device of the character described comprising a housing,spaced conducting members therein adapted to be connected to oppositesides of a high voltage source, an intermediate grounded conductingmember, an electrostatic charge responsive leaf suspended from eachfirst named member to swing toward the grounded member to establish anarc discharge between said members in said housing, and heat responsiveelements on said grounded member movable toward the other members inresponse to the heat from said are discharge to establish a lowresistance path between said members, said leaf comprising a thin stripof aluminum.

6. A safety device of the character described comprising a housing,spaced conducting members therein adapted to be connected to oppositesides of a high voltage source, an intermediate grounded conductingmember, an electrostatic charge responsive leaf suspended from each ofthe first named members to swing toward the grounded member to establishan arc discharge between said members in said housing, and heatresponsive elements on said grounded member movable toward the othermembers in response to the heat from said arc discharge to establish lowresistance path between the grounded member and said first namedmembers, said housing having means to support the grounded member andone of said first named members at a plurality of points differentlyspaced from the other of said first named members.

LEWIS H. LAMONT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,874.40? Young Aug. 30, 19321,939,019 Ouriefl Dec. 12, 1933

